1. Field of the invention
The present invention relates to a transmission for a tractor, and more particularly to a transmission for a tractor in which a main transmission part arranged between a forward/reverse transmission part and a sub transmission part is shortened, thereby reducing the whole length thereof.
2. Description of the Prior Art
Generally, a transmission for a tractor is formed in type of a series of transmission parts that are connected in order from an engine. That is, the transmission generally includes a forward/reverse transmission part that changes a direction of rotating power of the engine to a forward/reverse direction, a main transmission part that changes speed in four-stage at an output side of the forward/reverse transmission part, and a sub transmission part that changes speed in two to four-stage at an output side of the main transmission part. The transmission includes a power take-off (PTO) transmission part that draws power for driving an attachment installed on a rear side of the tractor.
In connection with such a transmission, Korean Patent Registration No. 0373595 (Feb. 12, 2003), and Japanese Patent Nos. 3266720 (Jan. 11, 2002) and 3422430 (Apr. 25, 2003) have disclosed a power shift type transmission in which the transmission device of the main transmission part is automated using a hydraulic clutch instead of a conventional synchromesh unit.
In such a transmission, although the power shift type is introduced to the main transmission for convenience of transmission, a series of all 4 gears are arranged longitudinally in a single row, i.e., in forward and reverse directions, so that a problem is caused in that length increment due to introduction of the power shift causes the main transmission part and therefore the whole transmission to increase in length thereof. In this way, as the length of the transmission is lengthened, a distance between a front wheel and a rear wheel becomes far away to problematically increase a minimum turning radius as well as to hardly secure installation space for a device for other additional function. For example, if the sub transmission part is intended to include a first sub transmission part changeable in speed in two-stage and further a second sub transmission part (e.g., ultra low speed transmission part) changeable in speed from the first sub transmission part, it is impossible for the above conventional transmission to secure the additional installation space for the second sub transmission part.